At present, there is such a rapidly growing demand of subscribers for communication services that various wireless communication technologies, and related network in which the wireless communication technologies are applied, have emerged, e.g., 2G/3G/4G mobile communication technologies and networks capable of providing wide coverage, and Wireless Fidelity (WiFi) technologies and Wireless Local Area Networks (WLANs) capable of providing hotspot coverage. Due to widespread applications of the various networks, there are scenarios in which different types of wireless communication network coexist, e.g., a scenario in which the 2G or 3G or 4G network coexists with the WLAN. In the scenario in which different types of wireless communication network coexist, a User Equipment (UE) typically makes reasonable selection among the types of network in order to be better served and to save its power. At present there is a technology among cellular communication network technologies to hand over the UE from the 2G or 3G or 4G network to the WLAN so as to offload a service to the WLAN so that the UE is provided with the data service.
An Evolved Packet System (EPS) is a system supporting various access technologies, and mobility between the various access technologies. In the multi-access scenario, the UE may be covered jointly by a number of 3rd Generation Partnership Project (3GPP) and/or non-3GPP access networks, which may operate with different access technologies or may be served by different operators or may provide accesses to different core networks.
For example, FIG. 1 illustrates a scenario in which a Universal Mobile Telecommunication System (UMTS)/Long Term Evolution (LTE) system coexists with the WLAN in the prior art. There are Access Points (APs) of a number of WLANs in a coverage area of an access control network node in the UMTS/LTE system (e.g., a Node B in the UMTS or an eNB in the LTE system), where a coverage area of each access point is smaller than that of the base station.
FIG. 2 illustrates a network architecture in which the UMTS/LTE system interoperates with the WLAN currently supported in the scenario above, where the interoperation in the architecture is achieved via an S2c interface between a Packet Data Network (PDN) Gateway (GW) and the UE. Here both the PDN GW and the AP of the WLAN can exchange information with a server in the Internet.
Further to the network scenario and architecture above, there exists a network selection mechanism implemented under an Access Network Discovery and Selection Function (ANDSF) policy. Particularly FIG. 3 illustrates the architecture of communication between the ANDSF and the UE, where the UE interacts with the ANDSF via an S14 interface which is an interface based upon the Internet Protocol. The UE and the ANDSF communicate in two modes including pull and push modes, where the UE transmits a request on its own initiative to the ANDSF in the former mode, and the ANDSF pushes information on its own initiative in the latter mode. The ANDSF policy is relatively static.
Network discovery and selection related information provided for the UE under the ANDSF policy in the prior art includes the following three categories information:
The first category of information relates to an Inter-System Mobility Policy (ISMP).
The ISMP includes a series of operator defined rules and preferences, and this policy defines whether to allow inter-system mobility, the most appropriate type of access technology to access the Evolved Packet Core (EPC), different priorities of different access technologies, and other information. The ISMP can be preconfigured in the UE or can be transmitted upon being requested by the UE or can be pushed to the UE by the ANDSF under some trigger. For example the ANDSF can issue a policy with the priority of the WLAN being higher than that of the LTE network, so that the WLAN system will be selected preferentially for an access when the UE is covered by both of the networks.
The second category of information relates to Access Network Discovery Information (ANDI).
The ANDSF can provide the UE with a list of access networks, available in proximity thereto, of a requested type of access, and related parameters, e.g., access technologies (e.g., Worldwide Interoperability for Microwave Access (WiMAX), etc.), identifiers of radio access networks, carrier frequencies, etc.
The third category of information relates to an Inter-System Routing Policy (ISRP).
The ISRP includes some information required for inter-system routing, and for a UE with a multi-radio access interface, e.g., a UE supporting IP Flow Mobility (IFOM) or Multi-Access PDN Connectivity (MAPCON), the information can be used to determine:
a) Which of the available access networks to transmit data when a particular routing condition is satisfied; and
b) When to prohibit access to some access network for a particular IP data flow and/or a particular Access Point Name (APN).
As specified in the existing protocol, the ANDSF selects the ISMP, the ANDI and the ISRP to be provided to the UE, as required by the operator and according to a roaming protocol, and the ANDSF can provide all of these three policies or can provide only a part of the policies. The ANDSF can interact with some database in the operator network, e.g., a Home Subscriber Server (HSS), etc., to retrieve information as required.
When the UE receives information about an available access network with a higher priority than that of the current access network, the UE shall perform a discovery and reselection procedure to be handed over to the access network with the higher priority if this is allowed by the user. When the UE selects the access network automatically, the UE can not access the EPC through an access network marked as prohibited in the ISMP.
In an existing measurement mechanism in the WLAN system:
As per the IEEE 802.11 protocol, related measurement available in the WLAN include: a channel load measurement to measure the utilization ratio (load) of a channel, which can be derived statistically over an idle period of time in some period of time; a noise histogram measurement to return a histogram of non-IEEE 802.11 noise power in a sampled idle channel; and a link measurement, which is a measurement of a radio frequency characteristic, to reflect an instantaneous quality of a link.
In the existing heterogeneous network scenario, offloading for the UMTS/LTE network to the WLAN is performed generally in two scenarios of seamless offloading and non-seamless offloading as illustrated in FIG. 4 and FIG. 5, where seamless offloading refers to that there is a connection between the WLAN and the 3GPP Core Network (CN), and the service via the air interface subjected to offloading is still directed to the 3GPP (including UMTS/LTE) core network; and non-seamless offloading refers to that there is no connection between the WLAN and the 3GPP CN, and the service via the air interface subjected to offloading is directed to the Internet directly without going through the 3GPP CN.
For offloading to the WLAN, a part of services requested by the UE may be transferred, or all the services requested by the UE may be transferred, and if a part of the services requested by the UE is transferred, then the UE will be connected with both the UMTS/LTE network and the WLAN; or if all the services requested by the UE are transferred, then the UE will be connected with only the WLAN after the service is transferred.
In the prior art, it has been only specified how to perform handover from the 3GPP network to the non-3GPP network, but it has not been specified how to perform handover from the non-3GPP network to the 3GPP network; and moreover the UE selects the network under the relatively static ANDSF policy, so when the UE is provided with the data service over the non-3GPP network after selecting the network, the UE still needs to be provided with the data service over the non-3GPP network even if the quality of the service available over the network is degraded, so that the problem of degrading the quality of communication, and even dropping a call, of the UE may arise.